Generally, a transmission is an apparatus that receives the input power from a driving power source, changes it into rotating speed suitable to driving conditions, and transmits it to an output shaft. The type of transmissions include the manual transmission with which a driver achieves his desired gear shift by manipulating a gear shift lever and the automatic transmission in which it automatically achieves an adequate gear shift based on the speed of the car and the opened degree of the throttle valve. The manual transmission has high fuel efficiency but is difficult to manipulate, while the automatic transmission is easy to manipulate but has low fuel efficiency.
Generally speaking, the greater the number of gear shifts that the transmission has, the higher the fuel efficiency of automobile can be obtained. Since the automatic transmission, however, includes a plurality of planetary gear sets and friction elements for manipulating each of the actuating means, the greater the number of gear shifts, the greater the number of the planetary gear sets and the friction elements becomes. This results in weight increase of the automatic transmission, hence lowering the fuel efficiency. So, the number of gear shifts in the automatic transmission is smaller than that of the manual transmission.
Besides, some additional devices used in an automobile et cetera, have to keep working even when not travelling, so they are directly connected to their driving power sources. Since a damper clutch is however disposed between the driving power source and the input shaft, it is not able to connect the additional devices to the input shaft. Therefore space for the additional devices is insufficient.
To solve above mentioned problems, some methods had been proposed to realize a plurality of gear shifts by inputting the rotating speed of a driving power source to one actuating means of a planetary gear set and inputting the rotating speed of a gear-shifting power source to the other another actuating means of the planetary set.
According to the above methods, however, the torque of the driving power source is applied to the gear-shifting power source, which results in serious loss of the torque. In addition, the rotating speed of the driving power source is directly input to the planetary gear set without decelerating of speed, which results in a problem that the gear-shifting is hard if the gear-shifting power source do not provides strong torque.